The human body is supplied by a complex network of blood vessels as part of the vascular system. The blood vessels are fluid conduits allowing for flow and distribution of blood throughout the body, and are generally arranged into arterial and venous sub-systems, which are themselves hierarchically arranged from larger ma supply vessels down to small capillary pathways. A primary function of the blood flowing through the vessels is to carry and distribute oxygen and other nutrients to the organs and tissue of the body. Another function of the blood is to collect waste products from the organs and tissue. Mechanically, the general organization of the vascular system is that of a hydraulic supply and return network with the heart providing the pumping and control to drive oxygenated blood to the organs and tissue in arteries, and to return blood from the organs and tissue in veins. Capillaries form the lowest functions on the hierarchy of vasculature, including the actual chemical (oxygen) exchange, and connect the arterial portion of the vascular network with the venous part of the vascular network.
As it carries oxygen, nutrients and waste products within the entire body, the vascular system has been recognized as a good vehicle for introducing drugs into the body, and as a good vehicle for extracting meaningful (blood) samples representative of the condition of the body. Since many primary vessels run slightly below the surface of the skin, they are accessible for procedures to introduce a substance into the blood or to extract a sample of blood from the vessels. For example, a common procedure is to introduce a drug or a fluid into the blood stream intravenously using an intravenous (“IV”) line. Glucose and antibiotics are examples of things commonly injected into a patient's veins using an IV line. In practice, a medical professional inserts a needle through the skin and through one wall of a relatively large and accessible vein and the injected fluid is released into the vein through the IV needle under pressure. The converse (blood sampling) is used by pulling blood from a vein, or allowing the blood to flow out of the vein and into the needle, to draw a blood sample from a patient these procedures can be painful to people, as they involve sticking the patient with a needle. Also, inaccurate placement of a needle can lead to improper delivery of the drug or fluid, and can cause unwanted injury to vessels and tissue in the vicinity of vessels. It is therefore preferable that the needle be inserted accurately and hit its mark without undue retries. The present discussion of veins can where applicable be extended to other types of fluid vessels, for example, arteries, capillary vessels, etc.
One type of clinical procedure using the location of the appropriate vessels is the insertion of a central line, also called a central venous catheter (“CVC”). A central line is a catheter, or tube, which is inserted into a vein and physically passed through the vein to the thoracic (chest) portion of the vena cava or the right atrium of the heart. The vena cava is a large vein delivering blood to the heart. Again, proper administration of a CVC benefits from knowledge of the location of the vessels of interest.
It is therefore useful to develop methods and systems for accurate location and imaging and detection of vessels, especially to assist in medical diagnoses and procedures that employ the blood vessels such as in the applications mentioned above. It would be especially useful to overcome present limitations and provide systems that combine accuracy, clinical relevance, comfort, and at the same time are relatively inexpensive, reliable, and not excessively cumbersome. This disclosure addresses some or all of these issues.